Fatigue Life Assessment For The Boom Of Crawler Crane Based On Fuzzy Damage

Boom is an important bearing member of the crawler crane, it often endures alternating load because of the operation of lifting, luffing and slewing. And the boom is space truss structure, it is easy to cause fatigue failure due to the effect of alternating loads and the existence of stress concentration at the connection between brace and chord. The problem is more prominent in the small-sized crawler cranes which are used frequently.The current liner fatigue damage accumulation theory such as traditional Miner’s rule and fuzzy Miner’s rule are not accurate enough in prediction of fatigue life. This paper proposes a Miner’s rule based on fuzzy damage, it takes not only the fuzzy damage cased by the stress near the fatigue limit which is familiar in fuzzy Miner’s rule, but also the fuzzy of critical damage caused by load sequence (including load size) into account. This method has been applied to the fatigue life prediction of the boom in a50t crawler crane. The main work of this paper is as follows:(1) A Miner’s rule based on fuzzy damage is proposed, basing on this method, a mathematical model at random loading is established, and then the model’s accuracy is compared with the traditional Miner’s rule and fuzzy Miner’s rule.(2) To decide the usage of common conditions and its proportion of the crawler crane, the50t crawler crane’s usage statistics is analyzed. The possible fatigue position of the boom is selected by analyzing the stress of the boom by finite element analysis software ANSYS, and then the load spectrums of these dangerous positions are gained.(3) The material’s S-N curve is modified according to the characteristics of the boom structure and the load on it, and a modified S-N curve is gained.(4) The fatigue lives of dangerous positions on the boom are calculated according to the load spectrum, modified S-N curve and the miner’s rule based on fuzzy damage.(5) A crawler crane’s boom fatigue life prediction program which is based on the method proposed in this paper is developed by software MATLAB.The Miner’s rule based on fuzzy damage which is proposed in this paper provides a new method for fatigue life assessment under random loading. And the approach of fatigue life assessment for the boom also has certain actual application value.